1. Field of the Invention
The present invention relates to a Broadband Wireless Access (BWA) system, and more particularly to a method for supporting various multiple antenna schemes in a system using an Orthogonal Frequency Division Multiple Access (OFDMA) scheme.
2. Description of the Related Art
In the current wireless mobile communication system, extensive research is being conducted into a high quality multimedia service capable of transmitting mass storage data at a high speed. Different from wire channel environments, wireless channel environments are subject to a distortion of the actual transmission signals due to various factors such as multi-path interference, shadowing, wave attenuation, time-varying noise and interference. Fading due to the multi-path interference is closely related to the mobility of a reflector or a user terminal. Accordingly, the actual transmission signals are mixed with interference signals and mixed signals are received. Because the received signals already represent a serious distortion of the actual transmission signals, the entire performance of a mobile communication system may deteriorate.
Fading may also distort the amplitude and phase of the received signals, and may become a main factor that disrupts the high speed data communication in wireless channel environments. Therefore, extensive research is being conducted in order to solve the fading problem. In order to transmit data at a high speed in a mobile communication system, it is necessary to minimize loss and any user-by-user interference resulting from the characteristics of a mobile communication channel. One of the technologies proposed in order to solve the afore-described problems is a Multiple Input Multiple Output (MIMO) technology.
The MIMO technology may be classified according to the data transmission schemes used and whether the channel information is fedback.
First, the MIMO technology may be classified into a Spatial Multiplexing (SM) technique and a Spatial Diversity (SD) technique according to the data transmission schemes. The SM technique is a technique for simultaneously transmitting different data by means of multiple antennas in a transmitter and a receiver, thereby transmitting data at a higher speed without increasing the bandwidth of the system. The SD technique is a technique for transmitting the identical data through multiple transmit (Tx) antennas, thereby achieving the Transmit Diversity (TD).
The MIMO technology may also be classified into a closed-loop scheme, in which channel information is fedback from a receiver to a transmitter, and an open loop scheme, in which channel information is not fedback from a receiver to a transmitter.
Referring to the current standard documents 802.16-REVd&D5, REVe/D5-2004 of the Institute of Electrical and Electronics Engineers (IEEE) 802.16e standard, only a scheme for supporting the MIMO technology using the open loop scheme has been proposed.